248 



0. "SI. WEN YON. 



exhibited a peculiar polymorphism. In the central part of the 

 hangiiij^ drop, where the fluid whs deep, the flagellates had 

 the typical ]iear-shaped appearance, with the long, ta]iering, 

 posterior extremity. At the sides of the hanging drop, where 

 there was only a thin layer of moisture on the cover-glass, the 

 typical pear shape was lost and the flagellates had the appear- 

 ance of amccbae. When first I observed this I thought my 

 culture had become contaminated with an amoeba, but the 



Text-fig. .5. 



Ordiiiaiy free-swimming type. 



presence of the long anterior flagelhim and the short posterioi* 

 one disproved this idea. It was possible to watch a single 

 individual swimming in the deep part towards the edge. On 

 reaching the shallow part the character of the organism 

 changes at once to the amcsboid form. Pseudopodia are pro- 

 truded and withdrawn, and the animal creeps about in a 

 typical amoeboid manner. All this while the long anterior 

 flagellum is lashing to and fro, but appears powerless to draw 

 the animal across the surface of the cover-glass. It is only in 

 the deeper part of the hanging diop that the flagellum is useful. 

 The posteiior flagellum is often not visible, and its prolonga- 

 tion across the surface of the bodv is more difficult to detect. 



